1. Field of the Invention
The present invention relates to a printing cylinder, such as a blanket cylinder (roller), a plate cylinder (roller), a feed roller for transferring ink from an ink reservoir onto a plate cylinder, etc., used for various printing machines such as an offset rotary press, etc.
2. Description of the Prior Art
A printing machine in the prior art is constructed so that printing ink, supplied in an ink reservoir, is transferred from one roller to another in an inking roller group (not shown in a figure), consisting of many rollers like feed rollers etc., in which adjacent rollers make rolling contact with each other via their outer circumferential surfaces. The ink is distributed appropriately during the transfer process to form a thin ink film, and then, as shown in FIG. 12, it is transferred on a printing plate 2, which forms a printing face and is wound around a plate cylinder 1. The ink is further transferred from the printing plate 2 to a blanket 4 fitted around the outer circumferential surface of a blanket cylinder 3. Then printing is performed on each side of a running web 5 with the blanket 4 while the respective blanket cylinder 3, disposed above and below, makes rolling contact with the running web 5 via its outer circumferential surface.
If ink is supplied to, and transferred by, only one of the blankets 4 of the blanket cylinders 3 disposed above and below a sheet path line 6 along which the web 5 runs, printing on one side only of the web 5 can be performed. If plural sets, usually 4 sets, of the blanket cylinders 3 are arrayed in parallel along the running direction of the web 5, multi-colored printing can be performed.
As the printing plate 2 used for printing by the printing machine is required to be changed each time according to what is to be printed on the web 5, a slit groove 7 is formed on the outer circumferential surface of the plate cylinder 1 along its entire axial directional length, so that the printing plate 2, on which a rectangular printing surface is formed, is wound around the plate cylinder 1 with the front and rear ends of the printing plate 2 inserted and gripped (fixed) in the slit groove 7.
As to the blanket 4 fitted to the blanket cylinder 3, in printing machines, before being improved to the printing machine shown in FIG. 12, like the printing plate mentioned above, a slit groove was formed on the outer circumferential surface of the blanket cylinder 3, and the front and rear ends of the blanket 4 were inserted therein so that the blanket was fitted to the blanket cylinder 3.
In a modern commercial offset rotary press, however, a printing machine using a cylindrical blanket 8 as the blanket 4, as shown in FIG. 12 and in FIG. 13, which is a detailed sectional view of the blanket cylinder 3 seen from arrows 13--13 of FIG. 12, has been put to practical use.
By use of such a cylindrical blanket 8, length Sa of a nonprinted portion in the running direction of the web 5 shown in FIG. 14 can be greatly reduced. Thereby loss of paper can be reduced and the cost of printing paper can be saved.
In a printing machine as shown in FIG. 13, the cylindrical blanket 8 is formed in a sleeve shape so as to be attached to and detached from the outer circumferential surface of the blanket cylinder 3. One of the bearing portions supporting both ends of the blanket cylinder 3 can be taken out so as to form a space so that attachment and detachment of the cylindrical blanket 8 is facilitated.
In the blanket cylinder 3, a through hole 10 is provided through the central axis portion of the blanket cylinder 3 so as to open at each end of the shaft, and an air blowing hole 11 is provided in the radial direction of the blanket cylinder 3 so as to pass from the through hole 10 to the outer circumferential surface. Compressed air introduced from the outside via the through hole 10 passes through the through hole 10 and the air blowing hole 11 to be injected outside in the radial direction of the blanket cylinder 3. A compressed air film is thereby formed in a gap formed between the outer circumferential surface of the blanket cylinder 3 and the inner circumferential surface of the cylindrical blanket 8, and thus attachment and detachment of the blanket 8 is further facilitated.
In the blanket cylinder 3, during normal printing operation, the supply of compressed air to the gap is stopped and the blanket 8 keeps close contact with the blanket cylinder 3 without slippage.
A slit groove for fitting the blanket, which was necessary to be formed on the outer circumferential surface of the blanket cylinder 3, similar to the slit groove 7 provided at the plate cylinder 1 shown in FIG. 12, thereby becomes unnecessary.
By the blanket 4 being wound around the blanket cylinder 3 being improved to the cylindrical blanket 8 attachable to and detachable from the blanket cylinder 3 as well as by the slit groove 7, or the gap width, of the plate cylinder 1 being made smaller, changes in the pressing force caused by shocks of the meshing of gaps or other various shocks have been greatly mitigated.
These shocks mainly involve those shocks generated as motion (vibration) in the radial direction of the plate cylinder 1 and the blanket cylinder 3 and those shocks generated as changes in angular velocity (rotation irregularity) in the rotational direction. Generation of these shocks will be a cause of duplication, slur, shock mark, gear mark, etc., that is, various printing obstacles, such as inking irregularities, color slippage, periodically generated belt-like printing irregularities, etc. on the printed surface.
But, by the improvement in using the cylindrical blanket 8, shocks accompanying the rolling contact of the plate cylinder 1 and the blanket cylinder 3 have been greatly reduced, and a printing machine which is capable of high quality printing and high speed operation has been realized.
Further, in relation to this improvement, as well as the improvement of making the width of the slit groove 7 smaller, or of making the slit groove unnecessary, it has become possible to make the rigidity of the plate cylinder 1, the blanket cylinder 3, etc. smaller.
Accordingly, without the necessity of using stronger rollers, there is an advantage in that, not only a compact size of the driving means, but also a compact size and reduced weight of the entire printing machine become possible.
As mentioned above, presently recent printing machines have made remarkable technical progresses.
In printing machines as shown in FIG. 12 as so improved, however, there is a customer need for further improvement in the reduction of the loss of paper and enhancement of production efficiency by way of enlarging the machine width, that is, enlarging the width of the web 5 to be printed.
That is, in FIG. 14, while the printing of 16 pages has been performed on both sides of the web 5 in the prior art, as shown by solid lines, by one rotation of the blanket cylinders 3, disposed above and below as in FIG. 12, a multi-page printing by one rotation of a blanket cylinder 31 is sought so that, by the machine width being enlarged, the printing of 24 pages on both sides of web, as shown by one-dot and dash lines, can be performed.
By such an improvement, the following effects are being expected:
(1) A paper loss portion 12 at each widthwise marginal end of the web 5 is reduced in amount in relative ratio to the entire width. That is, the paper loss portion 12 caused at the printing of every 16 pages is now caused at the printing of every 24 pages, so that the ratio of paper loss portion 12 is reduced.
(2) A folded binder becomes multi-page, and a bookbinding line can be made intensive.
(3) Further enhancement of productivity can be attained.
For realizing these requirements, however, it is necessary to elongate the length in the axial direction, from L to L', of the printing cylinder 20 used for printing, including the blanket cylinder 3 and the plate cylinder 1. The elongation of the printing cylinder 20 involves a large problem of deflection deformation of the printing cylinder 20 at the time of printing. That is, in addition to vibration occurring at the rotating shaft of the printing cylinder 20, there is caused a large problem of non-uniformity of the pressing force, represented by a nip pressure, between the central portion and both end portions of the printing cylinder 20.
The deflection deformation of the printing cylinder 20 occurs in a form as shown in FIG. 15. But if, for example, the cylinder diameter is to be enlarged for enhancement of deflection strength as a countermeasure for resolving the non-uniformity of the pressing force, there occur other problems relating to the size increase of the cylinder diameter and ancillary equipment, like bearings, etc., and the capacity increase of a motor as a driving means, as well as the size increase of the entire printing machine.